Neurodevelopmental diseases (NDDs ? Autism Spectrum Disorder (ASD), Intellectual Disabilities, Bipolar disorders, and Schizophrenia, etc.) are prevalent and due to errors in neurodifferentiation and neurocircuitry. While NDDs, in many cases, are due to inherited mutations, evidence is mounting that prenatal exposure to environmental toxicants also cause NDDs via disruption of epigenetics (e.g., modifications of histones [histone tags] or methylation of DNA). Our project will develop the Microscopic Imaging of Epigenetic Landscape- NeuroDevelopment (MIEL-ND) assay, which will enable testing of chemicals for epigenetic effects related to NDDs. In preliminary research by Alexey Terskikh (Sanford Burnham Prebys Medical Discovery Institute) MIEL methods were developed in which human Neural Precursor Cells (NPCs, from fetal brain) were treated with test compounds and analyzed for changes in the pattern of histone tags within the nuclei (altered ?epigenetic signature? ? which utilizes multiplexed immunolabeling, automated high throughput imaging, and cell-by-cell analysis using machine learning). A subset of chemicals from the US EPA ToxCast program was analyzed, and ?epigenetic hits? were identified. In a separate approach, Vala Sciences Inc, which commercializes cell-based assays relevant to toxicology/drug discovery, tested EPA compounds on synapses/neurite formation in neurons developed from induced pluripotent stem cells (iPSC-neurons), which represent human neurons in early stages of maturation. When results from the assays were compared, several epigenetic hits also altered synapse and neurite formation in the iPSC-neurons consistent with the hypothesis that epigenetic alterations may alter fate decisions of NPCs and neurodevelopment. To further develop the MIEL-ND, we propose to screen additional ToxCast compounds for effects on epigenetic and cell fate NPCs and test the compounds for effects on synapse/neurites in iPSC-neurons to develop a library of epigenetic hits with known effects on the two cell types. We will use these data and emerging data from the ToxCast program, to develop and optimize the MIEL-ND to predict NDD-inducing effects of possible environmental toxicants. The MIEL- ND will identify compounds that affect neurodevelopment that are not cytotoxic (which are missed by current assays) and represents a less expensive, higher throughput, more predictive alternative to current tests which use animals, thus reducing the use of animals in toxicity testing. Phase II goals include developing a version of the MIEL-ND featuring iPSC-NPCs (enabling use of cells derived from patients with NDDs), and adaptation of the assay to identify potential therapeutics for NDDs.